1. Field of the Invention
The present invention refers to a display for digital/analogous visualization of computer stored and bitmapped still or moving images on or by means of at least one visualization medium, the display consisting of a matrix including at least two sets of individually addressable electrodes, being arranged in rows and columns having crossing points and being connected to at least one control unit, for multiplexing, scanning or pulsating control signals from the control unit, whereby a temperature variation is obtained in the crossing points of the electrodes, which temperature variation is conducted towards a medium, substantially including a thermosensitive indication means for transforming the temperature change to visible dots.
2. Description of the Related Art
In certain applications, such as price indicators in shops, information indicators at shop windows or the like, advertising signs and other fields requiring visualization of information, there is a need for a display means, which can be manufactured in large quantities with low cost. The major problems with the LCD (Liquid Crystal Display) and TFT (Thin Film Transistor) screens are that a large number of displays are discarded due to sensitivity of the manufacturing process.
It is known in the art to write visual information on a thermosensitive display medium, where the medium becomes transparent when heated and opaque when cooled down or when heated above a certain temperature. The thermosensitive material of such a medium is also referred to as a thermochromatic material. The visualization materials used in thermosensitive displays are generally liquid crystals, for example encapsulated liquid crystals, which become transparent when heated, thus enabling incident light to be transmitted through the medium.
The international patent application WO 94/26528 discloses a display for the visualization of still or moving images, where temperature changes are produced by a pattern of resistive elements and transformed to visible dots in a visualization medium. The display comprises a matrix having at least two sets of electrodes, which sets cross each other and are distanced from each other by means of at least one resistive and/or inductive spacer means. The electrodes are arranged in rows and columns, which do not necessarily have to be perpendicular to each other. The matrix is further connected to at least one control device for multiplexing, scanning or pulsating the control signals. The electrodes are individually addressable according to the electric signals from the control unit and are arranged so that, when the selected electrodes in both sets of electrodes are energized, temperature changes are obtained at the cross points of the charged electrodes. The temperature changes (heat) are conducted towards the display medium, which comprises a thermosensitive indication means, such as a layer, a body or the like. The surfaces of the display then transform the temperature changes to visible dots or the like.
U.S. Pat. No. 4,837,071 discloses an information display medium comprising a thermosensitive material layer which can reversibly repeat turbid (opaque) and transparent conditions by being heated to different temperatures, and can keep one of the conditions stably below a particular temperature. The thermosensitive material layer is backed by a colored layer, another layer and a background panel. At least one of the mentioned layers is colored in different color patterns. The temperature of the thermosensitive material layer is controlled for displaying an image in a combination of different colors.
The document WO 92/01565 discloses an erasable optical display medium for colored visual information, which display medium comprises a substrate carrying a heat-sensitive film which can be converted to different optical states (opaque/transparent) under the influence of temperature. These states are permanent at normal ambient temperature (room temperature) and reversible by heating to specific temperatures. The display medium is designed to have a matrix of dots, the dots being combined into groups of four dots, where each of the four dots has a different primary color (e.g., red, yellow, blue or black). If the heat-sensitive film over a dot is converted, by appropriate warming, to the transparent state, the dot underlying the film becomes visible. This makes it possible to display colored data on the display medium.
U.S. Pat. No. 3,637,291 shows a display in which enclosed liquid crystals are used as image carrying medium, which crystals have two optical states, i.e., a first translucent state and another opaque state. The crystal layer becomes translucent first when it is exposed to a momentary electric field, since the visible image is created by increasing the temperature in the desired points, which become opaque. This device consists of many parts to be controlled, and the control method includes several stages for production of a visible dot.
Through U.S. Pat. No. 4,922,242, a visualization means for visualization of a pre-manufactured form is known. The visualization means consists of two electrodes with a resistive layer between them. A thermochromatic layer is provided between a pigment layer and a transparent polymeric layer. The image, such as a digit to be shown, is cut out as a metallic mesh. When an electric current passes through the electrodes, the resistive layer is warmed up. The heat is guided to the thermochromatic layer, which becomes translucent due to the heat, whereby the pigment layer becomes visible. This type of display is not flexible, must be formed in a predetermined shape, and cannot show moving images.
U.S. Pat. No. 3,410,999 discloses a display screen which includes a layer of liquid crystalline material of the cholesteric phase in which a temperature image is applied thereto according to electrical information by means of glossy elements provided in intimate contact with the liquid crystalline material. The display according to this document uses a liquid crystalline material of the cholesteric phase in which the brightness of the display is proportional to the amount of viewing light including ambient lighting directed onto the screen. The liquid crystalline material of the cholesteric phase exhibits curious changes in light reflecting properties when heated or cooled through a transition region near their melting point. Thus, the display according to this document uses the changes in reflectivity (changes in color). The display also needs a cooling arrangement.